1. Field of the Invention
The present invention is generally related to a paper overlaid wood board and, more particularly, to a paper overlaid, oriented strand board which has a smooth surface and is resistant to wood stain migration. The invention also relates to a method of making such a paper overlaid wood product.
2. Background Description
Oriented strand board is commercially available from a number of companies including J. M. Huber Corporation, Georgia-Pacific Corporation, Louisiana-Pacific, and a number of other sources. This material includes a plurality of wood xe2x80x9cflakesxe2x80x9d or xe2x80x9cstrandsxe2x80x9d bonded together by a binding material such as phenol formaldehyde resin or isocyanate resin together with sizing materials such as paraffinic waxes. The flakes are made by cutting thin slices with a knife edge parallel to the length of a debarked log. The flakes are typically 0.015 to 0.035 inches thick, although thinner and thicker flakes can be used in some applications, and are typically less than one inch to several inches long and less than one inch to a few inches wide. The flakes generally are longer than they are wide. In the fabrication of oriented strand board, the flakes are first dried to remove water, and are then coated with a thin layer of binder and sizing material. The coated flakes are then spread on a conveyor belt in a series of layers.
The layers of oriented xe2x80x9cstrandsxe2x80x9d or xe2x80x9cflakesxe2x80x9d are subjected to heat and pressure to fuse the strands and binder together. The resulting product is then cut to size and shipped. Typically, the resin and sizing comprise less than 10% by weight of the oriented strand board product. The fabrication of oriented strand boards is described in U.S. Pat. No. 5,525,394 to Clarke et al., and that patent is herein incorporated by reference. Oriented strand board has been used in sheathing walls, wooden I-beam structural supports, and in roofs and floors where strength, light weight, ease of nailing and dimensional stability under varying moisture conditions are the most important attributes. Oriented strand board is sold at a substantial discount compared to structural grades of soft plywood. The cost advantage of OSB over plywood is expected to increase as lumber shortages are expected due to limited resources.
However, the rough surface of OSB is undesirable in certain applications. For example, when OSB is used as flooring, the rough surface interferes with the attachment of a floor covering thereto. Further, individual strands are known to xe2x80x9cpop up.xe2x80x9d This makes the installation of surface covering materials, such as vinyl, hardwood flooring and ceramic tiles more difficult.
One way to alleviate such problems is to sand the rough OSB surface. However, even with sanding, imperfections on the surface of the OSB may create an undesirable appearance and negatively affect the affixation of a floor covering thereto. Further, the exposed surface of the OSB is susceptible to water damage.
Another known method to hide the defects on the surface of the OSB is to cover the same with a wood veneer comprised of plywood. Securing a wood veneer to the surface of the OSB has its drawbacks. For example, it tends to be relatively expensive. Additionally, the wood veneer often contains surface defects itself. Moreover, in order to protect the wood veneer and the OSB core from damage caused by exposure to wet conditions, the surface of the wood veneer must be treated.
It should also be noted that when vinyl floor covering is installed directly onto a wood sub-floor or wood veneer, wood stains have the propensity to migrate from the wood into the vinyl causing discoloration of the vinyl sheet. These wood stains result from extractives usually found in the cambium or outer part of a tree which is adjacent to its bark. The types and amount of extractives vary with different types of woods and it is noted that Aspen and Southern yellow pine have substantial amounts of extractives capable of migrating, thereby staining adjacent materials. One way of curing this problem is to remove the outer layers of wood before using the remainder to product xe2x80x9cstrandsxe2x80x9d. This, however, is not cost-effective and is wasteful of natural resources. Another way of dealing with the discoloration problem is to use an underlayment between the sub-floor and the vinyl covering, Obviously, this undesirably increases the cost of covering the floor.
In order to overcome the deficiencies of the prior art discussed above, there is provided a paper overlaid wood board that has a generally smooth surface and is not readily susceptible to water damage or stain migration. At least one surface of the oriented strand board core is covered with a resin impregnated paper overlay. The paper overlay preferably has a basis rate of about 25 lbs./msf to about 75 lbs./msf and a resin content of about 20% to about 60%. The finished board has a density ranging of about 35 lb/ft3 to about 55 lb/ft3, a modulus of rupture (MOR) of about 3000 to about 9000 psi, a modulus of elasticity (MOE) of about 0.4xc3x97106 to about 1.2xc3x97106 psi, and a thickness of about 0.25 inches to about 1.25 inches.
Other features and advantages will be readily apparent from the following detailed description of preferred embodiments thereof.